Fibrous electrostatic effects

Fibrous or particulate filters are not important anymore because membrane filters are relatively compact and perform very well. For filtration by straining, there is an intermediate air velocity at which filtration efficiency is a minimum because different collection mechanisms predominate at different ranges of velocity. At low velocities, diffusional and electrostatic forces on the particle are important, and increased velocity shortens the time for them to operate. At high velocities, inertial forces that increase with air velocity come into play below a certain air velocity, their effect on collection is zero. Surges or brief power failures could change velocity and collection efficiency... 

Nanofibre enhances the capture of nanoparticles such as viruses, bacteria, and man-made particles, such as soot from diesel exhaust. As soon as a fluid (air or liquid) contacts a nonwoven web, molecules are subjected to various forces, such as Brownian di siou, direct interception, partial impact, electrostatic forces, and sedimentation. For nanometre-scale fibres, a second factor has to be taken into account the effect of slip flow at the fibre surface. For macroscale fibrous materials, filtration mechauisms rely on continuous flow around the fibre, with a no-slip condition at the fibre surface. The theory starts to break down when the scale of the fibre becomes small enough that the molecular movements of the air molecules are significant in relation to the size of the fibres and the flow field. Using a slip-flow model at the fibre surface can extend the usefiil range of continuous flow theory. The Knudseu number (Kn) is used to describe the importance of the molecular movements of air... 

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